How to input specific force data into mocap example "Full Body.main"

[wuchangfa (changfa)]

Dear friends
recently,i meet some problem in experiment.because some reason,my lab can't synchronize infrared camera with force plateform.So,after experiment,we get two file:a .C3D file without force data from infrared motion capture system and a .txt file with force data.
we want use mocap example "Full Body.main" to do some inverse dynamics analysis.so have any way to input specific force data into "Full Body.main"?
very appreciate
2024.7.2
Wu

[dschander (Divyaksh S. Chander)]

Hi Wu,

The basic idea of applying external force is that you know the value of the force and you know where it is applied. The force plate is located precisely in a mocap lab so all of that information is saved in the c3d file. But if you know the sensor location and the force value, you can use an AnyInputFile class to read in the force file and apply it to the foot. However, it will be a little bit complex as you can't apply the force directly to the foot. You will need a dummy segment at the sensor location and some reactions between the dummy segment and the foot.

I think the most systematic way will be to try to use the ForcePlateAutoDetection class template like you have when the c3d file has the force data. To do that, you should try to feed in the values manually from your text file containing the force to the specific folder in your model tree. Specifically, you would need to recreate some information in Main.ModelSetup.C3DFileData.Groups.FORCE_PLATFORM.

Since, this specific folder will be already created by the c3d file, you won't be able to make changes in the original folder. Therefore, you must make a new folder where you mimic the structure of the force plate section of the c3d file. You will have to provide information like the number of force plates used, the data, force plate type, etc.

Then, when you use the force plate class, you can use the argument C3D_OBJECT to specify another folder where the class template expects the data from the c3d file.

But what you should do really depends on the data that you have available. I have just mentioned two options.

I hope this helps.

Best regards,
Dave